Dye-sensitized solar cells, DSSCs, have attracted significant interest in the past 30 years since the major breakthrough introduced by Prof. Grätzel and O’Reagan in 1991, with the demonstration of efficient charge separation and electron transport by high surface area TiO2 electrodes. The highest efficiency for a DSSC was reported in 2015 by kakiage et al. They engineered a co-sensitized system based on two dyes, the alkoxysilyl-anchor dye ADEKA and the organic dye LEG4, used the redox mediator [Co(phen)3]3+/2+ as the electrolyte, and designed a highly conductive CE based of FTO/Au/GNP, to obtain the impressive performance of 14.3% PCE.
Due to the large internal reorganization energy, cobalt-based electrolytes require driving forces for dye regeneration around 230 mV which represent a potential loss. In this regard, substantial attention has been attracted by copper-based electrolytes were the internal losses can be minimized to 0.2 eV, leading to higher open circuit voltages.
DSSCs with Cu(tmby)22+/1+ redox mediator have reached impressive open circuit voltages of 1.1 V as reported by Freitag et al. Recently, Cao et al., reported PCE’s exceeding 13% under 1 Sun intensity and outstanding 32% power conversion efficiency under 1000 lux intensity, placing DSSC as one of the most attractive technologies for ambient light (indoor) applications. Additionally, suppressing the use of liquid electrolytes in DSSC is a desirable feature toward commercialization and copper electrolytes can be efficiently used as solid HTM as introduced by Freitag et al, with the so-called zombie cells.
Our work on DSSC’s at LSPM currently focuses on two main areas:
Reducing internal energy losses at the main interphases of the cell to further improve the overall performance of the cells by means of:
- Design of novel donor−π-bridge−acceptor (D−π−A) dyes for a better compromise between driving force injection and alignment with the conduction band of the semiconductor.
- Development of new semiconductor materials with a higher conduction band (Fermi level) in order to improve electron injection from the LUMO of the dye and to further improve the VOC for copper-based electrolytes.
Stability studies of electrolyte mixtures to further extend the lifetime of cells to boost commercialization.
We are currently developing polymeric mixtures for quasi-solid electrolytes based on cobalt and copper complexes by formation of hyperbranched matrixes based on acrylate monomers. We study in-situ photopolymerization by UV curing methods to encapsulate the electrolyte in a hydrophobic network which can potentially increase the lifetime of the cells.
